1. Field of the Invention
The invention relates to an anti-creep device for use in a trailer suspension, and, more specifically, to a breakaway anti-creep device. The invention serves to retard the forward and downward movement of a trailer during loading, loss of air spring pressure, or other "stationary" times to limit the creep of the trailer from a loading dock or parked position and to breakaway if the load on the anti-creep device exceeds a predetermined amount to prevent damaging the suspension or trailer.
2. Description of the Prior Art
Many trailers have trailing arm suspensions with air springs to control the relative position of the frame with respect to an axle and also to cushion the relative movement of the axle toward the frame due to bumps in the road. In the loading or unloading of a trailer, the trailer is typically backed up against a dock by the tractor. The operator then lowers the front dolly legs on the trailer until they touch the ground and then removes the tractor. In storage situations the tractor may or may not be connected to the trailer. Although the air springs are pressurized by the tractor's air compressor during transport and stationary times, the air compressor is normally off during loading or unloading operations, preventing the addition or exhaustion of pressurized air.
As an empty trailer is loaded, the force from the weight of the goods being transferred to the trailer and the loading equipment, such as a forklift or a handcar, lowers the rear portion of the frame with respect to the axle. Because the compressor is off during the loading operation, the air pressure in the air spring is not adjusted to compensate for the increased load. While the rear portion of the trailer frame moves downwardly, the front portion of the trailer frame is substantially fixed at the height of the dolly and the trailer frame effectively rotates about the contact point of the dolly with the ground. The downward movement of the rear portion of the trailer frame results in the pivotal movement of the pivotal connection between the trailer frame and the suspension trailing arm. This pivotal movement results in the slight rotation of the wheel to move the trailer forward. In other words, the trailer tends to move away from the loading dock. This movement is referred to as "creep." Trailer creep can create hazards for loading.
One solution for trailer creep is to moveably mount a bar to the frame rail and move the bar to a use position between the frame rail and the axle or trailing arm. Since the bar extends between the frame rail and the suspension, it begins carrying the load of the trailer once the air spring sufficiently collapses to the point where the bar contacts the axle or trailing arm. Depending on the air spring type and capacity and the weight of the goods loaded in the trailer, it is possible to overload the trailing arm or axle through the bar, causing damage or failure. Also, if the bar is not rotated out of the way during vehicle operation, it can cause major damage to the trailer from bump inputs while going down the highway. International publication WO 97/37864 illustrates several examples of such an anti-creep device and is incorporated by reference.
Therefore, there is a need to reduce or eliminate the creep associated with a trailer during loading while preventing damage to the trailing arm or axle. The anti-creep solution must also be simple, reliable, and inexpensive if it is to be commercially viable. Further, the anti-creep solution must also not interfere with the normal function of the trailing arm suspension during its normal operation.